The present invention is directed towards an automatic lubricating system for applying lubricating fluid to one or more moving parts of an operating machine. More particularly, the present invention is directed towards an improved control circuit for controlling the operation of the automatic lubricating system.
FIG. 1 is a block diagram of a prior art automatic lubricating system 10 of the type sold by the assignee of the present application. The heart of lubricating system 10 is an electronic control circuit 12 which controls the operation of a fluid supply means 14 which distributes lubricant from a lubricant reservoir 16 to a main fluid line 18. The fluid supply means 14 is operable in both a first pressure mode, wherein it supplies fluid to main fluid line 18 at a rate which will nominally cause the pressure in the line 18 to be maintained at a relatively low level of, for example, 100-200 psi (hereinafter the normal operating pressure) and a second pressure mode wherein it supplies fluid to main fluid line 18 at a second, higher rate, which will nominally cause the pressure in line 18 to be maintained at a relatively high level of, for example, 300 psi (hereinafter the test pressure). As will be explained below, control circuit 12 switches fluid supply means 14 between these two pressure modes by either generating or not generating a pump solenoid signal PS.
The main fluid line 18 supplies lubricating fluid to a plurality of indicator blocks 20 which may take the form illustrated in U.S. Pat. No. 3,730,297. Under normal operating conditions, wherein fluid supply means is operating in the first pressure mode and the normal operating pressure prevails in line 18, each of the indicator blocks will divert a small percentage of the lubricating fluid in line 18 to one or more associated secondary lines 22 each of which terminates at an associated metering device 24. Metering devices 24 may be passive devices, such as a restricted orifice, or may be active devices which feed the lubricating fluid at predetermined times or at a predetermined rate (usually in drops per minute) to a respective machine part 26 of the operating machine being lubricated. As described below, the indicator blocks 20 also detect faults in either the secondary lines 22 or in the metering devices 24 whenever the system 10 is operated under test conditions (wherein the pressure in line 18 is increased to the test pressure level.
The downstream end of the main fluid line 18 terminates at a pair of pressure sensors 28, 30 which detect a fault condition under normal and test operating conditions of the lubrication system, respectively. The sensor 28 is a low pressure sensor and is used to detect faults in the main line 18 during normal operating conditions. This sensor will generate a low pressure fault signal P.sub.L whenever the downstream end of line 18 is below a first predetermined value (e.g., 50 psi) which is selected to be below the normal operating pressure. The sensor 30 is a high pressure sensor and is used to detect faults in either the secondary lines 22 or the meter devices 22 under test operating conditions. This sensor will generate a high pressure fault signal P.sub.H whenever the pressure of the downstream end of main line 18 is below a second predetermined value (e.g., 250 psi) which is substantially higher than the first predetermined value but less than the test pressure level. The high and low pressure fault signals are applied to control circuit 12.
The operator initiates operation of the lubricating system 10 by depressing a main power switch SWP which is a two position bistable switch which is connected between a main A.C. power source 31 (typically a 120 volt, 60 cycle A.C. line) and both the control circuit 12 and a motor starter 33. When the switch SWP is depressed, control circuit 12 is activated and motor starter 33 enables the operation of the motor of pump 29 which forms part of the fluid supply means. The pump 29 pumps fluid from lubricant reservoir 16 at a predetermined rate (typically in cubric centimeters per minute) to a two position solenoid valve 35. Solenoid valve 35 connects the output of pump 29 to either a bypass valve 37 or a check valve 39 under control of a pump solenoid signal PS generated by control circuit 12. When the pump solenoid signal PS is not generated, the solenoid valve 35 is disabled and connects the output of pump 29 to the bypass valve 37. Bypass valve 37 is preferably an adjustable valve which enables the operator of system 10 to control the flow rate at the output of the valve by adjusting a bypass lever which controls the percentage of input fluid which is returned to the reservoir 16. The flow rate at the output of valve 37 will be the flow rate into the valve less the flow rate back to the reservoir 16. The operator of system 10 will adjust the position of the bypass lever so that the pressure in line 18 will be, in the absence of any faults in the distribution system, at normal operating pressure. At this pressure, the desired amount of lubricating fluid will be applied to machine parts 26 but indicator blocks 20 will not be able to detect a fault in either the secondary lines 22 or in the metering devices 24.
In the event of either a blockage or an opening in the main line 18, the pressure at the downstream end of line 18 will fall below the pressure being sensed by low pressure sensor 28 causing the sensor 28 to generate the low pressure fault signal P.sub.L. Control circuit 12 responds to this fault signal by enabling a fault light 41 which provides the operator of system 10 with an indication that a fault condition exists. The operator would normally respond to the enabling of lamp 41 by turning off the machine being lubricated and depressing power switch SWP so as to disable the lubricating system 10.
While the low pressure sensor 28 will detect faults in the main line 18, it will not detect faults in the secondary lines 22 or in the metering devices 24. In order to detect such faults, control circuit 12 periodically places fluid supply means 14 in the second pressure mode wherein the pressure in line 18 is increased the test pressure level at which the indicator blocks 20 will sense faults in their associated secondary lines 22 and metering devices 24.
Circuit 12 achieves this result by generating the pump solenoid signal PS which enables the solenoid valve 35 and thereby causes the output of pump 14 to be applied to check valve 39. Check valve 39 is non-adjustable and ensures that the pressure in line 18 will rise to the test pressure level in the absence of any breaks in the fluid distribution system. This pressure is sufficiently high to ensure that indicator blocks 20 will detect any faults in the secondary lines 22 or metering devices 24. In the event that there is a break in one of the secondary lines or in the event that one of more of the metering devices 24 are not restricting the flow of lubricant to the machine parts 24, the pressure across the input terminal A and output terminal B of the associated indicator block 20 will fall below a preset level indicating a fault condition in either the secondary line 22 or the metering device 24. As described in U.S. Pat. No. 3,730,297, the indicator block 20 will respond to this fault condition by dumping a substantial portion of the lubricant in main line 18 to the atmosphere. If the secondary line 22 or the indicator block 24 is blocked, the internal pressure in the indicator block 20 between its input A and its output B will rise above a second predetermined level also indicating a fault condition. Indicator block 20 also responds to this fault condition by dumping a substantial portion of the lubricating fluid in main line 18 to the atmosphere.
Summarizing the foregoing, whenever one of the indicator blocks 20 detects a fault condition in one of its associated secondary lines 22 or metering devices 24, the indicator block 20 will dump a substantial portion of the lubricating fluid in main line 18 to the atmosphere with the result that the pressure at the downstream end of the main line 18 falls below the level being sensed by the high pressure sensor 30 and the high pressure sensor 30 will generate the high pressure fault signal P.sub.H. Control circuit 12 detects this signal as indicating a fault condition somewhere in the lubricating system and responds by enabling a fault indicator lamp 41 which informs the operator of system 10 that a fault condition exists. The operator would normally respond to the enabling of lamp 41 by turning off the machine being lubricated and depressing power switch SWP so as to disable the lubricating system 10.
While the automatic lubricating system 10 of the prior art has been generally successful, it exhibits several drawbacks. In the prior art lubricating system, the control circuit 12 continually monitors the low pressure pulse signal P.sub.L during those intervals when the pump 14 is first turned on. Since the pressure in main line 18 is not instantaneously increased to the normal operating pressure, this could result in the control circuit 12 erroneously enabling fault indicator lamp 41 and the operator might unnecessarily shut down the operation of both the lubricating system 10 and the machine being lubricated.
Another drawback of the prior art control circuit 12 is that it did not automatically shut off the machine being lubricated when an actual fault condition was detected with the result that if the user of the system 10 did not notice that the indicator lamp 41 had been enabled, the machine being lubricated could be severely damaged.
Yet another drawback of the prior art control circuits is that they can normally operate in only a single mode of operation. Different control circuits had to be provided to meet the differing needs of end users.